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From:   Kees Cook <keescook@chromium.org>
Date:   Sat, 6 Apr 2019 09:43:50 -0700
Message-ID: <CAGXu5jJGC1kB-0e3DimBSprcgEBnWRB=i287g-9T5a-RidFqBg@mail.gmail.com>
Subject: Re: [PATCH v3 bpf-next 00/21] bpf: Sysctl hook
To:     Andrey Ignatov <rdna@fb.com>
Cc:     Network Development <netdev@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Roman Gushchin <guro@fb.com>, kernel-team <kernel-team@fb.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Jann Horn <jannh@google.com>
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On Fri, Apr 5, 2019 at 12:36 PM Andrey Ignatov <rdna@fb.com> wrote:
>
> v2->v3:
> - simplify C based selftests by relying on variable offset stack access.
>
> v1->v2:
> - add fs/proc/proc_sysctl.c mainteners to Cc:.
>
> The patch set introduces new BPF hook for sysctl.
>
> It adds new program type BPF_PROG_TYPE_CGROUP_SYSCTL and attach type
> BPF_CGROUP_SYSCTL.
>
> BPF_CGROUP_SYSCTL hook is placed before calling to sysctl's proc_handler so
> that accesses (read/write) to sysctl can be controlled for specific cgroup
> and either allowed or denied, or traced.
>
> The hook has access to sysctl name, current sysctl value and (on write
> only) to new sysctl value via corresponding helpers. New sysctl value can
> be overridden by program. Both name and values (current/new) are
> represented as strings same way they're visible in /proc/sys/. It is up to
> program to parse these strings.
>
> To help with parsing the most common kind of sysctl value, vector of
> integers, two new helpers are provided: bpf_strtol and bpf_strtoul with
> semantic similar to user space strtol(3) and strtoul(3).
>
> The hook also provides bpf_sysctl context with two fields:
> * @write indicates whether sysctl is being read (= 0) or written (= 1);
> * @file_pos is sysctl file position to read from or write to, can be
>   overridden.
>
> The hook allows to make better isolation for containerized applications
> that are run as root so that one container can't change a sysctl and affect
> all other containers on a host, make changes to allowed sysctl in a safer
> way and simplify sysctl tracing for cgroups.

This sounds more like an LSM than BPF. So sysctls can get blocked when
new BPF is added to a cgroup? Can the BPF be removed (or rather,
what's the lifetime of such BPF?)

-- 
Kees Cook